Magnetic sensors are increasingly important in various industries. For instance in the automotive industry various sensors such as parking sensors, angular sensors e.g. in throttle valves, ABS (Anti-lock Braking System) sensors and tire pressure sensors can be found in modern vehicles for improving comfort and safety. Magnetic sensors are particularly important in automotive applications, because magnetic fields penetrate easily through most materials. Unlike for example optical sensors, magnetic sensors are also highly insensitive to dirt.
Several different magnetic sensor technologies are currently available, such as sensors based on the Hall Effect and sensors based on the magnetoresistive effect such as anisotropic magnetoresistive (AMR), tunnel magnetoresistive (TMR) and giant magnetoresistive (GMR) sensors.
For the next generation of magnetic automotive sensors the structures of corresponding magnetic elements are planned to be monolithically integrated on top of active silicon (i.e. a semiconductor chip having implemented an integrated circuit) in order to reduce packaging costs, to reduce the number of bond pads and to make a matching of magnetic/electrical elements easier/more accurate. This integration requires a new processing route for the magnetic sensor elements on the top metal layer of an integrated circuit e.g. in a CMOS back-end process.
In case of a magnetic sensor module relying on the AMR effect the magnetic sensor elements are made from a permalloy material which is a nickel-iron magnetic alloy with about 20% iron content and 80% nickel content. Interconnects are required to connect the magnetic sensor elements consisting of thin permalloy stripes to the underlying integrated circuit. The main challenge for a monolithic integration is to perform the patterning of the permalloy stripes and the interconnect formation, which serve as the electric connection to the underlying active silicon (e.g. an application-specific integrated circuit (ASIC)) without damaging each other. Specifically, in case a magnetic sensor element patterning is performed before a formation of the interconnects, the magnetic sensor elements need to be prevented from any damage during the process of exposing of the interconnects. Vice versa, if the interconnect formation is performed before patterning of the magnetic sensor elements, the exposed metal of the interconnects must not be damaged by the permalloy patterning process.
Particularly, a microwave resist strip and a sidewall polymer removal step after etching of contact holes for forming the interconnects as well as a sputter etch before deposition of the contacting metal could damage the magnetic sensor elements if they are formed first. This is because the permalloy is exposed during these steps. Vice versa, a patterning of the magnetic sensor elements could damage the interconnect areas if they are formed at least partially before the magnetic sensor elements. Particularly, the exposed metal of the interconnects could be damaged either by an acid if the material of the magnetic sensor elements is etched wet or by an ion bombardment of a dry etch process.
There may be a need for providing an effective and reliable manufacturing procedure for a magnetic sensor module having magnetic sensor elements monolithically integrated at or on a semiconductor chip such that the risk of damaging either magnetic sensor elements or interconnects is significantly reduced.